The present invention relates to a conductive electrolessly plated powder used, for example, for bonding small electrodes of electronic devices and the like, its producing method, and a conductive material containing the plated powder. Specifically, the present invention relates to a conductive electrolessly plated powder, its producing method, and a conductive material used for a conductive adhesive, an anisotropic conducting layer, and an anisotropic conductive adhesive or the like for conducting and bonding the confronting connecting circuits.
Heretofore, as a conductive powder used for a conductive adhesive, an anisotropic conducting layer, an anisotropic conductive adhesive or the like, metal powder such as nickel, copper, silver, gold, solder and the like; carbon series such as carbon powder, carbon fiber, carbon flake and the like; and conductive plated powder coated with metal such as nickel, nickel-gold, copper, gold, silver, solder and the like to the surface of a resin core particle with electroless plating, vacuum deposition and the like, are known.
The conductive powder using the metal powder mentioned above is large in specific gravity, as well as amorphous in shape, and wide in particle size distribution. Therefore, when such powder is used by being mixed with various matrix materials, the purpose of the product becomes limited because the sedimentation or dispersion of the powder is extremely difficult.
The conductive powder using the carbon series powder mentioned above is not used in a purpose requiring high conductive property or high reliability, because the conductivity of the carbon itself is small.
The conductive powder using the conductive plated powder mentioned above is generally produced with a method of dipping the core powder to a plating solution prepared in beforehand, performing plating reaction for a period of time determined by an empirical supposition, and stopping the reaction. The electrolessly plated powder having projections to the surface thereof is easily obtained with such method. However, when the core to be plated is a granule or a powder having large specific surface, autolysis of the plating solution occurs, so that the obtained electrolessly plated powder becomes mixed with fine nickel resolvents.
Also, because a strong aggregate is formed, the aggregate is cracked with physical technique or the like. This results in breaking of the aggregates and a phenomenon of exposing the uncovered surface.
An example of an electroless plating method for a powder or powdery core solving such problem includes a conductive filler consisting of an electrolessly plated powder with fine metal particles deposited and formed as thick and substantially continuous coating to the surface of an organic or a mineral base material using electroless plating method, which the applicant of the present invention had developed earlier (Japanese Patent Laid-Open No. H1-242782).
The electrolessly plated powder obtained by the above-mentioned method has the plated fine metal particles deposited and formed as a thick and substantially continuous coating to the core powder, with the shape of the coating excelling in flatness, without forming bumps. Therefore, it is possible to provide excellent high conductive property, when the powder is used for the conductive adhesive, the anisotropic conducting layer, and the anisotropic conductive adhesive or the like.
However, the electrolessly plated powder obtained in the method mentioned above has a flat surface. Therefore, for example, when the powder is used for a conductive adhesive and the like for adhering circuit boards formed with aluminum wiring patterns in a condition where the aluminum wiring patterns confront each other, there are cases where good conductivity cannot be obtained. This is because the surface of the aluminum wiring pattern is normally formed with 3-9 nm of oxide coating, so that the powder cannot break through the oxide coating, as well as the contact area becomes small.
Also, the Japanese Patent Laid-open No. H4-36902 discloses a method of producing conductive particulates by performing metal plating to the surface of non-conductive particulates that has projections at the surface thereof.
However, the conductive particulates mentioned above is characterized in its core, with the projections formed to the surface of the particulates (mother particles) indicating a flat surface by a method of adhering using an adhesive or welding directly the child particles of the same material or of a different material, or by a method of adhering the child particles to the surface of the mother particles by putting the mother particles in a rotating container and evaporating the solvent while rotating the container, and the like, and with the metal plating being provided to the surface of the particles thereafter. With such structure, the conductive particulates mentioned above suffers from defects such as the child particles easily detaching by ultrasonication used for dispersion and the like during plating pretreatment process and the like, resulting in occurrence of dispersion in the surface condition after plating. Therefore, the conductive particles mentioned above cannot obtain good conductivity constantly.
The present invention solves the problems mentioned above, with the aim of providing a conductive electrolessly plated powder having a good conductivity with respect to connection between conductive patterns or between electrodes having an oxide coating thereon, a method of producing such powders in a manner advantageous industrially, and a conductive material containing the electrolessly plated powder.
That is, the present invention provides a conductive electrolessly plated powder formed with nickel or nickel alloy coating with electroless plating to a surface of a spherical core particle having an average particle diameter of 1-20 xcexcm, wherein said plated powder includes small projections of 0.05 to 0.4 xcexcm on an outermost layer thereof, and said coating is substantially continuous with said small projections.
Moreover, the present invention provides a method of producing a conductive electrolessly plated powder, the method comprising:
a catalyzing treatment process of carrying palladium to a surface of a spherical core particle by first capturing the palladium ion to the surface of the spherical core particle and reducing the same;
an A process which is an electroless plating process of adding an aqueous slurry of the spherical core to an electroless plating bath including nickel salt, reducing agent, compelxing agent and the like; and
a B process which is an electroless plating process of adding components of an electroless plating solution divided into at least two solutions, respectively, to an aqueous slurry of the spherical core simultaneously and sequentially; wherein at least both of said A process and B process are carried out after said catalyzing treatment process.
Further, the present invention provides a conductive material using the conductive electrolessly plated powder.